1. Field of the Invention
The present invention relates to an indentation testing instrument and indentation testing method.
2. Description of Related Art
There has been known an indentation testing instrument, as a material testing machine, which forms an indentation on a specimen surface by pressing an indenter shaft provided with an indenter on a tip thereof into the specimen surface to evaluate a mechanical property such as a hardness of material (for example, see Japanese Patent Application Laid-Open Publications No. 2004-12178).
For example, the indentation testing instrument measures an indentation depth (displacement amount of the indenter) at the time when a tip of the indenter is pressed into the specimen surface with a predetermined load by a displacement gauge to evaluate the mechanical property such as the hardness of material based on a relation between the displacement amount and the load.
Since the indentation depth measured by the indentation testing instrument includes a machine frame distortion amount (machine frame compliance) due to a distortion of a machine frame of the testing instrument itself caused by the load applied to the specimen by the indentation testing instrument, it is established to perform a correction for removing the machine frame compliance, for example, by a standard such as ISO14577.
However, for example, since a method introduced in ISO14577 is a correction method based on a principle that a compliance which is an inverse of an initial unloading slope and an inverse of a square root of a contact area calculated from a curve are expressed as a linear expression passing through zero and which method presumes the machine frame compliance based on a specimen stiffness obtained from a test result, there is a problem that a correction value sometimes includes an error due to the presuming method.
Moreover, since the indentation testing instrument of Japanese Patent Application Laid-Open Publications No. 2004-12178 measures the machine frame distortion by a first displacement gauge and measures the indenter indentation depth by a second displacement gauge, a plurality of displacement gauges are needed.